This is the guidance -
www.gov.uk/government/publications/actions-for-schools-during-the-coronavirus-outbreak/guidance-for-full-opening-schools#res
They don't have to offer full live lessons, but should, amongst other things -
"In developing their remote education, we expect schools to:
use a curriculum sequence that allows access to high-quality online and offline resources and teaching videos and that is linked to the school’s curriculum expectations
select the online tools that will be consistently used across the school in order to allow interaction, assessment and feedback and make sure staff are trained in their use
provide printed resources, such as textbooks and workbooks, for pupils who do not have suitable online access
publish information for pupils, parents and carers about their remote education provision on their website by 25 January 2021 – an optional template is available to support schools with this expectation
set work that is of equivalent length to the core teaching pupils would receive in school, and as a minimum:
primary: 3 hours a day, on average, across the school cohort
secondary: 4 hours a day, with more for pupils working towards formal qualifications this year
provide frequent, clear explanations of new content, delivered by a teacher or through high-quality curriculum resources or videos"